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Topic: Hints to a Pd/C Hydrogenation?  (Read 16623 times)

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Offline BobfromNC

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Re: Hints to a Pd/C Hydrogenation?
« Reply #15 on: November 29, 2012, 02:31:10 PM »
Part of how you do this depends on scale and what apparatus you are using.   If you have mgs to a gram, you could do the entire reaction in small RBF using a ballon of H2 as the source of H2.  If you are doing more than that, you might want to use a Parr type shaker or other similar apparatus.  I would always have someone help me the first time on any system.   

I also recommend EtOH rather than MeOH, it does not catch fire as easily (seen a few myself) and is safer in several ways.   You can always add EtOAc as well for many cases.   Most people use 10% Pd/Carbon, safer than 20%, and use the wet stuff.   

Lastly, I do use Celite sometimes, but for SMALL scales, once you have purged the reaction well with N2, I like to suck the reaction up into a plastic syringe (trying to leave most of the catalyst) and then filter through a small 0.45 micron syringe filter (Like a Gelman PTFE or similar one), which removes ALL of the carbon.   Then I add another shot of EtOH to the reaction with a clean syringe and then suck it up in to the used syringe and wash the syring and filter with that.   For small scales, I find that I lose less material than on Celite, and the material is not exposed much to air, if I do it properly, which is ideal for my substrate.

Offline Dan

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Re: Hints to a Pd/C Hydrogenation?
« Reply #16 on: November 29, 2012, 03:58:53 PM »
Another reason to avoid methanol is traces of formaldehyde in old bottles - you can end up methylating amines in your substrate by reductive amination. I used to work in alkoloid synthesis and always used ethanol, water or aqueous dioxane as the solvent.
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Offline discodermolide

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Re: Hints to a Pd/C Hydrogenation?
« Reply #17 on: November 29, 2012, 04:05:29 PM »
On scale (>50kg substrate) we had a problem with methanol, Exactly, it started to produce formaldehyde and then CO2 which poisoned the catalyst. We never saw this on a lab scale and funny plant results, lower yield, more catalyst required, longer reaction time etc.  led us to this side reaction after some weeks of experimentation.
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